1. Field of the Invention
The present invention relates to a radar transceiver particularly for cars and relates to a direct current voltage applying circuit to a high frequency line equipped in a bias applying circuit, IF (intermediate frequency) acquiring circuit or a micro-wave circuit and the like used in the radar transceivers.
2. Brief Description of the Related Art
FIG. 2 is a block diagram illustrating a constitution of a widely used radar system for cars. An antenna radiate radio beams in accordance with frequencies from an oscillator 3 arranged in a transmitter. A reflected wave from a target received by the antenna 1 is inputted to a frequency converter 5 via circulator 2, which has a function to separate the received wave and the transmitted wave. The reflected wave and a local oscillation generated by the oscillator 3 in a different frequency from the transmitted wave, are converted and outputted as an intermediate frequency (IF). The outputted IF is detected and amplified by a signal processing unit 6 for determining a position of the target, and the detected result is displayed on a displaying device D. More precise detection with less noise can be attained by converting the reflected wave into the IF. Thus a detecting method after converting the received wave into the IF, namely, a heterodyne detection is employed.
Usually millimeter waves are used in the radar systems for cars from viewpoints of a beam width, a measuring accuracy and dimensions of the radar system etc. Waves radiated from the antenna 1 arranged at the front end of the car are reflected by cars running ahead and processed for detecting positions of cars so as to avoid collisions with cars running ahead. Three widely used methods of measuring a distance to the target are shown in FIGS. 3A to 3C in the form of block diagrams.
A pulse radar system is shown in FIG. 3A. In the figure reference numeral xe2x80x9c11xe2x80x9d is an antenna, xe2x80x9c12xe2x80x9d is a transmitter, xe2x80x9c13xe2x80x9d is a stabilized oscillator, xe2x80x9c14xe2x80x9d is a range gate for measuring the distance, xe2x80x9c15xe2x80x9d is a synchronous detector, xe2x80x9c16xe2x80x9d is a pulse stretching circuit and xe2x80x9c17xe2x80x9d is a detector.
FIG. 3A shows the arrangement of a pulse Doppler radar system for measuring a relative velocity of the car to the target by utilizing Doppler shifts of carrier waves. This type of radar system can transmit and receive waves at different timings so as to execute a several number of detection simultaneously. However, in this system a high peaked output is required in order to attain a high detecting performance. In order to gain the detected distance with higher accuracy the heterodyne detection is required.
FIG. 3B shows a two-frequency (continuous wave) CW type radar system. In the figure reference numeral xe2x80x9c21xe2x80x9d is an antenna, xe2x80x9c22xe2x80x9d is a circulator, xe2x80x9c23xe2x80x9d is an oscillator, xe2x80x9c24xe2x80x9d is a modulator, xe2x80x9c25xe2x80x9d is a mixer, xe2x80x9c26xe2x80x9d is an amplifier, xe2x80x9c27xe2x80x9d is a synchronous detector, xe2x80x9c28axe2x80x9d and xe2x80x9c28bxe2x80x9d are BPF (band pass filter) and xe2x80x9c29xe2x80x9d is a phase sensitive detector.
This radar system simultaneously transmits two continuous waves having close frequencies and determines the distance based on a detected phase difference between Doppler components of reflected waves, and the relative velocity of the target based on Doppler frequencies of reflected waves.
FIG. 3C shows an FM-CW type radar system. In the figure reference numerals xe2x80x9c31axe2x80x9d and xe2x80x9c31bxe2x80x9d are antennas, xe2x80x9c32axe2x80x9d and xe2x80x9c32bxe2x80x9d are directional couplers for a transmitting side and a receiving side respectively, xe2x80x9c33xe2x80x9d is an oscillator, xe2x80x9c34xe2x80x9d is a frequency modulator, xe2x80x9c35xe2x80x9d is a mixer and xe2x80x9c36xe2x80x9d is an amplifier.
In this type radar system a transmitting wave is modulated in frequency form so as to obtain a triangular wave and the like. The frequency modulated transmitting wave and the reflected wave are mixed so as to gain a beat frequency, from which a distance to the target and a relative velocity to the target are detected.
The above-mentioned pulse Doppler radar system, two-frequency CW radar system and FM-CW radar system are constituted by combinations of several components. Each component such as oscillator, the modulator, the mixer and the amplifier etc. is constituted by a combination of electronic parts, which differs from types of the radar systems.
Since the combinations of a considerable number of components are employed in the above-mentioned conventional radar systems, it is rather difficult to obtain compact sized radar systems. Further specifically structured wiring such as a micro strip line, an NRD (nonradiative dielectric guide) and a wave guide etc. which are employed to connect the above-mentioned components, makes it more difficult to realize compact sized radar systems and direct part mountings on these radar systems.
Since conventional radar systems require a considerable number of parts, it is inevitable that the radar systems require high manufacturing costs, which are difficult to be reduced.
Since constitutions of the radar systems are different in different respective types of radar systems, even a component having similar function can not be employed in different radar systems.
In addition, a diredt current voltage applying circuit employed in a high frequency voltage line of the pulse Doppler radar has the following problems.
FIG. 5 is a generally used circuit diagram for applying a direct current voltage to the high frequency voltage line. In the figure, character xe2x80x9cAxe2x80x2xe2x80x9d is a high frequency input terminal, character xe2x80x9cBxe2x80x2xe2x80x9d is a direct current voltage input terminal and character xe2x80x9cCxe2x80x2xe2x80x9d is an output terminal for outputting a resultant voltage when the direct current voltage is applied to the high frequency line. Reference characters xe2x80x9cC1xe2x80x2xe2x80x9d, xe2x80x9cC2xe2x80x2xe2x80x9d and xe2x80x9cL1xe2x80x9d are respectively capacitors (Cxe2x80x2) and a choke coil (L).
The circuit shown in FIG. 5 employs a direct current supplying coupled circuit, where the direct current voltage is applied to the high frequency line via the choke coil L1. Since an impedance value of the choke coil L1 on the high frequency side is high, the direct current voltage can be applied to the circuit without a high frequency leakage from the terminal B and without any influences on frequency properties of the high frequency line.
However, in such conventional direct current voltage applying circuit where the choke coil is employed, there is a problem that a voltage with high frequency pulse can not be applied. In such circuit a transient phenomenon caused by the choke coil and the capacitor arranged at the direct current input terminal side, deforms pulse wave pattern as shown in FIG. 6B.
FIG. 6A shows a high pulse wave pattern P at the direct current input terminal side B where a pulse height is 5.5xe2x88x925.0=0.5V and a pulse width 36 ns (which includes 2 ns in the rise and fall duration respectively).
FIG. 6B shows a prior art pulse wave pattern Pxe2x80x2 at the output terminal C in a deformed state.
The present invention is carried out in view of the above-mentioned problems. One of the objectives of the present invention is to provide a simply constituted radar transceiver capable of being applicable to various types of radar systems, capable of making more compact system and capable of reducing its manufacturing costs without combining a considerable number of components.
And other objective of the present invention is to provide a direct current voltage applying circuit to a high frequency line where a pulse voltage pattern is kept in the same form as before application.
The radar transceiver according to the present invention comprises a negative resistance diode capable of varying oscillating frequencies according to applied voltages, where the negative resistance diode transmits a pulse wave and receives a reflected pulse wave by a target. The received reflected pulse wave is processed with a heterodyne detector so that the target is detected.
The oscillation from the negative resistance diode is modulated by variably controlling the voltage to be applied to the negative resistance diode.
The oscillation, the frequency modulation and the frequency conversion performed by respective components in conventional radar systems are replaced by one component, namely, the negative resistance diode. The negative resistance diode also can eliminate the circulator for separating the transmitted and received waves. Consequently a more compact radar system with less manufacturing cost is realized.
The direct current applying circuit to the high frequency line used in radar systems comprises a line element having a leakage power suppressing effect which is connected to the direct voltage input terminal.
An input terminal of the line element comprising a power distributor is connected to a high frequency wave input terminal and an output terminal of the power distributor is connected to a direct current voltage input terminal so as to attain the leakage power suppressing effect.
The above-mentioned power distributor is arranged as a Y-shaped power distributor in a distributed parameter circuit.